1. Field of the Invention
This invention relates to a damper interposed between a stationary portion and a supported member for preventing propagation of vibrations or impact from the stationary portion to the supported member.
2. Description of Related Art
Up to now, for preventing propagation of the vibrations and impact to the supported member, a variety of dampers have been proposed which are interposed between a stationary portion supporting this supported member and the supported member. Referring to FIG. 1, a damper 100, in which the stationary portion is an outer casing 101 of a disc player device adapted for reproducing information signals from a recording disc and the supported member is a disc reproducing unit 102 of the disc player device, includes a bag-shaped main body portion 106 formed of a flexible material. The material of the main body portion 106 is a synthetic resin material such as butyl rubber. The open end of the main body portion 106 is closed by a flat-plate-shaped lid 105 for defining a hermetically sealed hollow portion 107. This hollow portion 107 is charged with silicone oil 108 as a viscous liquid. This damper 100 has a columnar portion 109 formed as one with the main body portion 106 and positioned in the housed state within the hollow portion 107. This substantially columnar-shaped portion 109 has a shaft inserting hole 110 extending along its axis. The shaft inserting hole 110 has a hole opening to outside the damper.
This damper 100 has its lid 105 secured to the inner wall section of the outer casing 101 and has a pivot shaft 104 set on the outer wall section of the disc reproducing unit 102 fitted into the shaft inserting hole 110. If vibrations or impact are applied to the outer casing 101, the main body portion 106 is deformed, at the same time the silicone oil 108 flows in the hollow portion 107 to prevent or suppress propagation of the vibrations or impact to the disc reproducing unit 102, as shown in FIG. 2. At this time, a force is applied which tends to shift the disc reproducing unit 102 relative to the outer casing 101, as indicated by arrow F in FIG. 2, thus deforming the main body portion 106 while shifting the columnar portion 109 within the hollow portion 107. When the columnar portion 109 is shifted in this manner, the silicone oil 108 operates as a resistance for suppressing the movement speed of the columnar portion 109. This suppression of the movement speed by the silicone oil 108 suppresses or prevents propagation of the vibrations or impact to the disc reproducing unit 102.
That is, the gain of the vibrations propagated to the disc reproducing unit 102 from the outer casing 101 is maximum at a resonant frequency f.sub.0, as indicated by a rightwardly decreasing curve shown by a reference numeral (a) in FIG. 3. and becomes smaller the higher the frequency becomes than the resonant frequency f.sub.0. The transmission characteristics shown by the reference numeral (a) in FIG. 3 specify the acceleration the disc reproducing unit 102 is subjected to with respect to the acceleration of the vibrations applied from outside to the outer casing 101.
On the other hand, the anti-vibration characteristics of the disc reproducing unit 102 by itself are low at a higher frequency range than 20 to 30 Hz, as indicated by a reference numeral (b) in FIG. 3. This is because the resonant frequency of a recording disc, such as a compact disc "CD" (trade mark) itself is of the order of 100 Hz. The anti-vibration characteristics of the disc reproducing unit 102 specify up to which strength of the vibrations (frequency and amplitude) the satisfactory playback state of the recording disc is maintained without interruption of the playback sound (sound skip) during reproduction of the recording disc.
The anti-vibration characteristics of a disc driver, inclusive of a damper, at a pre-set frequency, as synthesized from the anti-vibration characteristics of the disc reproducing unit 102 by itself and the transmission characteristics of the damper, may be represented by the following equation (1): EQU .gamma.=.beta./(10.sup..alpha./20) (1)
As may be seen by a rightwardly rising curve, sufficient anti-vibration characteristics can be realized in a frequency range higher than about 20 to 30 Hz.
In the above damper 100, if the ratio of the outer diameter A of the columnar portion 109 indicated by .phi.A in FIG. 1 to the inner diameter B of the shaft inserting hole 110 shown by .phi.B in FIG. 1 (A/B) is as small as less than 2.3, the columnar portion 109 is deformed, as shown in FIG. 2, in case the disc reproducing unit 102 is shifted significantly relative to the outer casing 101, because the holding power of the columnar portion 109 is not sufficient to keep its own shape, thus occasionally producing a gap P between the inner surface of the shaft inserting hole 110 and the pivot shaft 104.
If the columnar portion 109 is deformed such as to produce this gap P, the multiplication factor of resonant vibrations corresponding to the gain of the vibrations propagated at the resonant frequency f.sub.0 among the transmission characteristics of the damper 100 is increased, thus raising the gain of the vibrations in the high frequency range. If the gain of the vibrations indicated by the reference numeral (a) in FIG. 3 among the transmission characteristics of the damper 100 is increased, the anti-vibration characteristics of the disc reproducing unit 102, inclusive of the damper 100, indicated by the reference numeral (c), are lowered, because the denominator of the above equation (1) is increased. Moreover, if the multiplication factor of resonant vibrations is increased, the amplitude of the disc reproducing unit 102 with respect to the outer casing 101 at the resonant frequency f.sub.0 is increased such that there arises the risk of the disc reproducing unit 102 impinging against the inner wall section of the outer casing 101. For evading this collision, it is necessary to provide a sufficient air gap between the disc reproducing unit 102 and the inner wall section of the outer casing 101. However, if a sufficient air gap is provided between the disc reproducing unit 102 and the inner wall section of the outer casing 101, the outer casing becomes bulky.
For lowering the multiplication factor Q of resonant vibrations, it may be contemplated to lower the consistency of the silicone oil 108, as provided in JISK2220, or to lower the hardness of the material of the main body portion 106. However, in this case, since not only the resonant frequency f.sub.0 but also the gain of the vibrations in the frequency range not lower than 20 Hz to 30 Hz are raised, the anti-vibration characteristics in the frequency range not lower than 20 Hz to 30 Hz among the transmission characteristics of the damper 100 cannot be improved sufficiently.
Conversely, the consistency of the silicone oil 108 or the hardness of the material making up the main body portion 106 may be increased for lowering the resonant frequency f.sub.0. However, in this case, the multiplication factor of resonant vibrations is increased such that again the anti-vibration characteristics of the disc reproducing unit 102 inclusive of the damper 100 in the frequency range not lower than 20 Hz to 30 Hz cannot be improved sufficiently.
For example, referring to FIG. 4 showing transmission characteristics of a damper having a higher consistency (that is lower viscosity) of the silicone oil 108 than that of the damper 100 shown in FIG. 3, the resonant frequency fo of the damper of FIG. 4 becomes smaller, however, its multiplication factor of resonant vibrations is increased.
Also, referring to FIG. 5 showing transmission characteristics of a damper having a still higher consistency (that is lower viscosity) of the silicone oil 108 than that of the damper shown in FIG. 4, the resonant frequency f.sub.0 of the damper of FIG. 5 becomes smaller further, however, its multiplication factor of resonant vibrations is increased further. Referring to FIG. 6 showing transmission characteristics of a damper having a yet higher consistency (that is, lower viscosity) of the silicone oil 108 than that of the damper shown in FIG. 5, the resonant frequency f.sub.0 of the damper of FIG. 6 becomes yet smaller further, however, its multiplication factor of resonant vibrations is still increased further.